A new acoustic transducer and measurement method have been developed for precise measurements of surface wave velocity. This technique is used to investigate the acoustoelastic effect of surface waves in polymethylmethacrylate (PMMA). The transducer utilizes two miniature conical PZT elements for surface wave transmitter and receiver, and hence can be viewed as a point-source/point-receiver (PS/PR) surface wave transducer. Surface waves are excited and detected with the PZT elements and the surface wave velocity can be accurately determined over a small measurement area. Improvement has been made so that the transducer can be used for both conductive and non-conductive materials. The transducer is then applied to measure the acoustoelastic effect of surface wave in a PMMA specimen. The acoustoelastic coefficients are experimental determined.

A technique for inverting residual stress based on a theory of acoustoelasticity is presented. A general incremental constitutive relation is first derived for a pre-stressed material subjected to an additional infinitesimal elastic deformation. The theory is then employed on using ultrasonic means to evaluate residual stresses of residually stressed materials. The residual stresses are assumed to be homogeneous in materials as usual. The only major assumption in this formulation is that the additional deformations caused by ultrasonic evaluating process are infinitesimal and elastic. No assumption on the origin of residual stresses is needed, nor the assumption on the possible existence of “natural state” of the materials. Successful inversion of residual stresses are demonstrated through a preliminary numerical experiment.